In typical commercial reproduction apparatus (electrographic copier/duplicators, printers, or the like), a latent image charge pattern is formed on a uniformly charged charge-retentive or photoconductive member having dielectric characteristics (hereinafter referred to as the dielectric support member). Pigmented marking particles are attracted to the latent image charge pattern to develop such image on the dielectric support member. A receiver member, such as a sheet of receiver member, transparency or other medium, is then brought into contact with the dielectric support member, and an electric field applied to transfer the marking particle developed image to the receiver member from the dielectric support member. After transfer, the receiver member bearing the transferred image is transported away from the dielectric support member, and the image is fixed (fused) to the receiver member by heat and pressure to form a permanent reproduction thereon.
One type of fuser device for typical electrographic reproduction apparatus includes at least one heated roller, having an aluminum core and an elastomeric cover layer, and at least one pressure roller in nip relation with the heated roller. The fuser device rollers are rotated to transport a receiver member, bearing a marking particle image, through the nip between the rollers. The pigmented marking particles of the transferred image on the surface of the receiver member soften and become tacky in the heat. Under the pressure, the softened tacky marking particles attach to each other and are partially imbibed into the interstices of the fibers at the surface of the receiver member.
Accordingly, upon cooling, the marking particle image is permanently fixed to the receiver member.
Most commercial electrographic reproduction apparatus are capable of reproducing images on receiver members of a range of widths, for example ranging from 8" to over 14". The fuser device therefore must heat any of these different width receiver members to the proper temperature range for good fusing. As a receiver member passes over the fuser roller, it absorbs and carries heat away from the roller. When the receiver member is narrower than the width of the fuser roller, the fuser roller heat is not removed from the roller in the areas beyond the receiver member width.
Typical fuser devices use a single lamp where the filament lengths are equal to or greater than the widest receiver member run in the reproduction apparatus. This produces a fairly uniform temperature distribution when the reproduction apparatus is making wide copies. However, when making narrower copies, excess heat beyond the receiver member edges causes the ends of the fuser roller temperature to rise.
Axial temperature uniformity along the fuser roller affects how well marking particles are fixed to the receiver member, receiver member handling performance, and fuser roller life. If there is non-uniform temperature on the fuser roller surface, the fixing quality on the receiver member will also be non-uniform. Further, fusing temperature affects fixing quality by how well the marking particles are melted and imbibed into the receiver member. Temperature uniformity affects fusing receiver member handling performance. A nip is formed between the fuser and pressure roller, the shape of which is predetermined to improve wrinkle performance. Any deviations from this shape can lessen the intended performance. The aluminum cores and elastomeric covers of the fuser rollers generally have high coefficients of thermal expansion. If the temperature is non-uniform, the thermal expansion of the rollers will be non-uniform and affect the nip shape accordingly. Accordingly, degradation of receiver member handling will result. Moreover, excessive fuser roller temperatures cause elastomeric covers to degrade causing loss of release characteristics and excessive hardening.